function getAjax(HttpUrl,callbackFn){
        
                var xhr = new XMLHttpRequest()

                xhr.open("GET",HttpUrl)
                //xhr.open("post","http://127.0.0.1:5500/18/03_%E5%AE%9E%E8%B7%B5/1ajax/wt.txt");
                
                xhr.send()
                //xhr.send("username = wt&password=123456");

                xhr.onreadystatechange = function(){
                if(xhr.status == 200&&xhr.readyState==4){
                   
                    callbackFn(xhr);
                    
                } 
            }

}   